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Two complexes based on phosphorescent viologen ligands have been synthesized. Complexes 1 and 2 not only possess reversible photochromic and electrochromic properties, but also exhibit fluorescence and persistent luminescence. They have potential applications in inkless print, color-changing films, data encryption, and anti-counterfeiting. [Display omitted] • Complexes 1 and 2 exhibit reversible photochromic and electrochromic behaviors. • Complexes 1 and 2 exhibit long-lived persistent phosphorescence. • Complexes show great potential in data encryption and anticounterfeiting. • Complexes have potential applications in inkless printing, color-changing films. Viologen-based complexes have garnered significant attention due to their multifunctional stimuli-responsive properties and tunable persistent luminescence. However, achieving ultralong afterglow emission and color change in these complexes remains a challenge, limiting their application in the field of persistent luminescence. Herein, two novel viologen-based complexes were successfully designed and synthesized using N,N′-bis(2-carboxyethyl)-4,4′-bipyridinium dichloride (H 2 bybpy) ligands and trimesic acid (H 3 BTC) with the transition metals Zn(II)/Cd(II). Complexes 1 and 2 display reversible photochromic and electrochromic properties. Interestingly, complexes 1 and 2 in their crystal state exhibit dual fluorescence and persistent luminescence, emitting a green and cyan afterglow when the UV lamp is turned off at 77 K. Incorporating phosphorescent molecules and changing the metal significantly extended the duration of persistent luminescence and altered the hue. The complexes were also demonstrated to have potential applications in inkless printing, color-changing films, data encryption, and anti-counterfeiting. This work enhances the application of viologen-based complexes in light-controlled persistent fluorescence and provides ideas for achieving ultra-long afterglow emission. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tuning phases of MIL-100, MIL-110 and MIL-96 by applying formic acid as modulator. • Demonstrating the diversity of various ligands on node sites of MIL-110 and MIL-96. • Illustrating a highly flexible formate bonding site on Al 3 (OH) 3 unit of MIL-96. • Elucidating only a small fraction of node sites contributes to catalysis. Metal oxide cluster MOF nodes are a good platform to understand the reactivities and catalysis. MIL-96, MIL-100 and MIL-110 are drastically different in their node structures. Following our previous reported results for MIL-100, we report the modified synthesis and characterization of the node sites of MIL-110 and MIL-96 and their catalytic sites by using methanol dehydration as probe reaction. We show that these MOFs can be synthesized from the same solution by adding various amounts of formic acid as modulator. Herein, the chemistry of hydroxyl, formate and methoxy groups were used to probe the three MOFs' node sites. IR data show the bonding structures of these ligands are highly diverse, with reactivities and flexibilities depending on node sites. We identified terminal OH group and various µ 2 -OH groups in single, paired or hydrogen bonded modes on the MOF nodes. Formate ligands were introduced to the node sites during the synthesis or by a post treatment in formic acid/DMF solution. Surprisingly, the bonding modes of formate ligands on Al 3 (OH) 3 node structure of MIL-96 can be reversibly switched between monodentate and bidentate through a process induced by water molecules. Further, methoxy ligands—likely to be the intermediate for catalytic reaction—were also observed on the node sites under methanol dehydration conditions at 250 ℃. The activities of MIL-100 and MIL-96 for methanol dehydration determined by TOF per node were similar, both approximately 3-fold higher than that of MIL-110. The data suggests that catalytic sites incorporate adjacent vacancy and defect node sites, which constitute a minority among all observed MOF node sites. We foresee the opportunities in expanding the chemistry and understanding into other MOFs with metal oxide cluster nodes. [ABSTRACT FROM AUTHOR]

[Display omitted] • A multi-ligand strategy was proposed to design high-efficient MOF photocatalysts. • The three-ligand MOFs, EY/NH 2 /H-MIL-125, were synthesized to verify our strategy. • The optimal three-ligand MOF can yield H 2 of 2.15 mmol g−1 h−1 under visible light. • Electron transfer is enhanced by a push–pull effect induced by the NH 2 -H 2 BDC and H 2 BDC ligands. • The third ligand EY facilitates the electron photoexcitation under visible light. The design and construction of high-performance photocatalysts with both strong visible light harvesting and effective electron transfer are highly desired in the photocatalysis field. Herein, a multi-ligand strategy based on the MOF materials is proposed. A three-ligand Ti-MOF EY/NH 2 /H-MIL-125 (ENHM) was prepared via a facile hydrothermal method, in which 2-aminoterephthalic acid (NH 2 -H 2 BDC), terephthalic acid (H 2 BDC) and Eosin Y (EY) were employed as three ligands. The push–pull effect induced by different substituent groups (–NH 2 and –H) on the skeleton of NH 2 -H 2 BDC and H 2 BDC promotes the efficient transfer of photogenerated electrons from organic ligands to metal nodes; while the third ligand EY increases the number of photoexcited electrons by enhancing the visible light absorption ability. Among the three-ligand MOF photocatalytic materials, ENHM-2 performs the optimal H 2 production activity of 2.15 mmol g−1 h−1, much higher than dual-ligand NH 2 /H-MIL-125 and EY/NH 2 -MIL-125 and single-ligand NH 2 -MIL-125. A probable mechanism was also proposed for the three-ligand MOFs. This multi-ligand strategy may open up a new direction toward the preparation of MOF-based photocatalytic materials with excellent photocatalytic performances. [ABSTRACT FROM AUTHOR]